Cathode-ray tube



March 3, 1953 J. M. CAGE cATHoDE-RAY TUBE Filed Deo. 22, 1950 BY W Patented Mar. 3, 1953 UNITED STATES PATENT OFFICE 2,630,543 cA'rHoDE-RAY TUBE John M. Cage, Montclair, N. J. Application December 22, 1950, SerialfNo. 202,245

This invention relates to image reproducing tubes and more particularly to projection type tubes for use with a suitable lens to project the images on a screen.

It is well known that second anode accelerating potentials of the order of 30,000 to\50,000 are required to obtain suicient brightness of the reproduced images on projection tubes to permit satisfactory projection. Higher voltages are of course desirable, but even at the lower voltages it has been found that conventional carbon coatings on the inside of the tube for shielding the electron beam, between the second anode and the screen, break down and produce gas in the tube that greatly impairs its usefulness. Carbon ycoatings have heretofore been required as the external magnetic deection and focusing coils for the beam were not materially affected by the carbon because of its high resistance. It has been observed that that part of the carbon or aquadag coating in the field of the deflecting and focuslng coils does generate substantial heat which probably results from the action of the high voltage as well as the magnetic elds. Excessive heating of the carbon or Vaquadag results in the generation of gas in the tube and greatly impairs its operation.

This invention eliminates carbon coatings altogether and in its place employs a low resistance;

shield of metal or the like that will not only withstand the high voltages without deterioration but, because of its structure and relationship to the magnetic iields, permits magnetic deflection and focusing means to be used with substantially the same efficiency attained with conventional carbon coatings. ages can be used without the danger of generating harmful gases and therefore enables the attainment of very much. brighter pictures,4

Another object of the invention is a newl and improved cathode ray tube structure. y

The above and other objects will become more apparent in the following description and accompanying drawings forming part of the applica` tion.

In the drawings- 1 Fig. 1 is a cross-sectional View of a tube in accordance with the invention; and

Fig. 2 is a cross-sectional view taken along the line 2 2 of Fig. l.

In the figures, I denotes the envelope of a projection tube having a front face I2, an enlarged cylindrical part I4 and a narrow necklike extension I6. In the end of the neck I6 is a conventional electron gun having a filament I8,

Thus very high accelerating volt- 7 Claims. (Cl. 313-76) control elements 20 and 22, and a second anode 24. These elements are supported by at least three insulating members 26 fastened to the envelope at a point within the base part 28. The front face I2 of the tube carries a luminescent screen 30 and may have a metallic coating thereon to protect the luminescent screen from ion burns. Surrounding the neck IE are the focusing and deiiecting -eoils 32 and 34 respectively. These coils are disposed at a point forwardly of the second anode 24.

The structure of the tube thus far described is conventional. Conventional tubes, however, employ a carbon coating on the inner wall of the large envelope section I4 and that part of the neck I6 forward of the anode 24. High voltage and engages and electrically contacts the second anode 24. Notwithstanding the presence of this tubular metallic member 42 in the magnetic fields, negligible losses are entailed over those that may be normally experienced with carbon coatings applied directly to the wall of the neck I6. This is attained by properly proportioning the external diameter of the shield 42 with the internal diameter of the coils 32 and 34. For instance, good results can be obtained with some loss when the outside ldiameter of the shield part 42 does not exceed one-half the internal diameter of the coils 32 and 34, while negligible loss is encountered if the shield doesv not exceed one-third the internal diameter of the coils. With. the latter proportion, the structure will permit suicient deiiection angle of the beam to be obtained for screens of the general size used in projection tubes and conventional deflection and focusing coils may be used; that is, coils of an internal diameter of the order of 1%. It is apparent, however, that this shield could also be used for direct view vtubes and, if desired, the coils could be modified by increasing the internal diameter to enable the attainment of very wide deflection angles and still employ the optimum ratio of shield diameter to coil diameter.

The shield 38 and its conical part 42 is held rigidly within the tube envelope I0 by the metallic ring or collar 40 on one end and the second anode 24 on the other. In this embodiment the collar 40 forms part of the beam shield. For ease in assembly, the conical part 42 may be slotted as shown at 44 to form a plurality of spring-like ngers for gripping the inside of the anode 24. The supporting ring or collar 40 is also formed with slots 46 formed in each edge thereof and the individual fingers 48 thus formed are curved as shown at 5|] so that they will 4slide relativeto the glass envelope without damaging or scratching the inner surface.

The shield 3S joins the collar 40 at a point midway of its edges and may be secured thereto by riveting, welding or other suitable means. As the front or screen edge of the collar 4llis in close proximity to the screen 30 the entire path of the electron beam from the second anode yto the screen is completely shielded.

The shielding structure is connected to lthe high voltage terminal 36 by the lead 52. By reason ofthe electrical contactbetween ngers 4 of theconical rshield section 42 and the'second anode, the latter fisalso maintained -at'the same potential and without -any resistance losses entailed'inthe use of high resistance carbon coatings in conventional tubes. The screen 3U is also charged-tothis high potential and the'connection between thescreen and the shield member 4B'is preferably Yaccomplished Aby a metallic coating `of silver, aluminum or the like extending from the periphery of the screen alongthe-wall ofthe cylindrical envelope section I4 vso that it'willbe contacted by the 4spring Vfingers 50 of the shield part Vlill.

With lthis structure all carbon and raquadag coatings within Vthe tube are entirely eliminated, thusenabling higher'voltages to beapplied to the second anode and rscreen ywithout the danger of generation of harmful gases and without l,entailing any losses in the magnetic deflection and focusing of the -beam greater than'those normally encountered with Ycarbon or aguadag coatings.

This Vapplication is .a vcontinuation inrpart Off my application SerialNo. 60,868, filed `November 19, '1948, and issued October A2, -19,51, as Patent #2,569,654.

l. A cathodegray tube `corriprising an outer lenvelope, an electron gunin one end ofthe envelope, a Ascreen in the other end of the envelope, a solid metallic self-sustainingshield extending from the screen to 4the electron gun to shield the beam throughout its travel from the gun ,to the screen, and magnetic beam controlling means about. the tube envelope and at ;a point between ,the gun and the screen, said shield having that Vpart encircled by the beam controlling rmeans of a diameter less than one-half'the inside ,diameter ofthe magnetic means.

2. A cathode ray tube of the magnetic deflection type comprising an outer envelope, an electron gun in oneend of the envelope for generating an electron beamya screen in the other end of said envelope, a vcontinuous shield for said beam'extending from the gun to the screen and 6a consisting of a stable material of high conductive properties, said shield being lspaced from the envelope throughout 'atleast a part of its length.

3. Means for shielding a cathode ray beam in an image reproducing tube of the magnetically defiected and focused type wherein coils are placed about the beam, comprising a continuous metallic self-sustaining shield surrounding the cathode ray beam and having a diameter at that part between the coils and the beam less than one-half the distance between opposing coils.

4. Means for shieldinga cathoderay beam in .an imagereproducing :tube of the magnetically deflected and focused type wherein coils are v.placed about the beam, comprising a continuous metallic self-sustaining shield surrounding the vcathode ray beam and having a diameter at that part between the coils and the beam approximately one-third the distance between opposing coils.

nA .cathode ray tube comprising an outer envelope having an enlarged cylindrical part and a small cylindrical part coaxially alined with said enlarged part, va-screengin the enlarged part,

an electron gun in vthe Ysmall part, including va tubular second Vanode element, and a cylindrical metallic shield extending from the screen to the second anode comprising a collar having a plurality of spring ngers about each edge thereof to bear lagainst the inner wall of the enlarged cylindrical part, a, first conical member fastened at its larger -end to said collar with its smaller end terminating adjacent the entrance of the small lcylindrical envelope part and la second anode conical member joined to the smaller end ofthe rst conical part-and extending toa-point within the tubular second anode.

16. Ina cathode ray1tube vhaving an evacuated envelope, a ygun rstructure therein including a second anode, a magnetic means surrounding the tube forwardly ofthe gun structure for deecting the electron beamgmeans for shielding the electron beam comprising a tubular continuous metallic member within lsaid envelope and spaced from the wall thereof at least in the region of said magnetic means, said member extending forwardly ofthe gun structure to a point beyond the magnetic defiecting means surrounding said tube and energized at a-potential at least'as high as that of the second anode.

L7. "Means for -shielding a cathode ray 'beam in an vimage reproducing tube of the'magnetically deiiected type -wherein coils are placed about the beam, comprising a continuous metallic shield within the tube envelope and surrounding the cathode ray beam, said shield extending beneath the'magneticfdefiection coils -andvspaced from the wall of said :tube at least in the region of the magnetic deflection coils.

."JOHN 'M. CAGE.

REERENCES `CITED The following references -are of record -'in nthe le of this patent:

.UNITED STATES PATENTS 

